Power converter apparatus provided with low-pass filter circuit for reducing switching frequency components

ABSTRACT

A power converter apparatus is provided to include a switching circuit, and a filter circuit. The switching circuit generates an AC voltage by switching a DC voltage at a predetermining switching frequency, and the filter circuit converts the AC voltage from the switching circuit into the DC voltage by low-pass filtering the AC voltage. The filter circuit induces first and second bypass capacitors, and an inductor. The first bypass capacitor bypasses noise of a first frequency component of the AC voltage from the switching circuit, and the second bypass capacitor bypasses noise of a second frequency component of the AC voltage from the switching circuit, which is lower than the first frequency component. The inductor is inserted between the first and second bypass capacitors, and the inductance thereof is set so that a resonance frequency of the filter circuit is lower than the switching frequency by insertion of the inductor.

TECHNICAL FIELD

The present invention relates to a power converter apparatus, such as aDC/DC converter apparatus, for example.

BACKGROUND ART

In a power converter apparatus that performs power conversion byperforming on/off control of a switching device, high-frequencyswitching noise generates due to turning on/off of the switching devicebecause switching control is performed at a switching frequency of 20kHz or more generally. As a result, there has been such a problem that afailure such as malfunction or function stop of electronic equipmentoccurs.

For example, FIG. 9 illustrates a configuration of a power converterapparatus 101 according to Conventional Example 1 as disclosed in PatentDocument 1. Referring to FIG. 9, the power converter apparatus 101includes a power supply filter circuit 110 and a voltage convertercircuit 120. In this case, the power supply filter circuit 110 includesa first filter circuit 111 including a capacitor 111 a, and a secondfilter circuit 112 including a series circuit of a capacitor 112 a andresistor 112 b, the filter circuit 111 and the second filter circuit 112being connected in parallel. In addition, the voltage converter circuit120 includes a switching circuit 121 including switching devices 121 aand 121 b, and a low-pass filter 122 including a coil 122 a and acapacitor 122 b.

It has been known that high-frequency ringing noise (100 MHz to a few100 MHz) generates in a frequency band in the output of a prior artpower converter apparatus due to an influence of a parasitic inductancethereof. In the power converter apparatus according to ConventionalExample 1 shown in FIG. 9, the first filter circuit 111 including a bulkcapacitor 111 a having a large capacitance, and the second filtercircuit 112 having a small capacitance capacitor 112 a for noisesuppression are added to reduce high frequency noise. This results instabilization of a drive pulse signal and reduction of high frequencynoise.

In addition, in the power converter apparatus according to ConventionalExample 2 disclosed in Patent Document 2, a high-frequency bypasscapacitor and a low-frequency bypass capacitor, which are provided in arear stage of a switching circuit, are connected with a relatively smallinductance. As a result, the power converter apparatus can operatewithin a high frequency region having relatively little switching noise.

PRIOR ART DOCUMENTS Patent Documents

[Patent Document 1] Japanese Patent Laid-open Publication No.JP2014-103842A; and

[Patent Document 2] Japanese Patent No. JP6207751B1.

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, in Conventional Example 2, there are a parasitic inductanceinevitably due to wiring (hereinafter, referred to as a wiringinductance) between the high-frequency bypass capacitor and thelow-frequency bypass capacitor. Therefore, a resonance phenomenon occursdue to these LC circuits.

FIG. 10 is a graph illustrating a relation between the resonancefrequency fr and the wiring inductance for describing a problem to besolved by the present invention. As illustrated in FIG. 10, the wiringinductance decreases as the resonance frequency fr changes fromswitching frequency f_(SW) toward an upper limit fr max of the resonancefrequency. However, there has been such a problem that switching noiseis further amplified by a resonance phenomenon in a case where theresonance frequency fr and the switching frequency f_(SW) match eachother.

In addition, it is predicted that, in the future, next-generation powerdevices will have to operate at higher frequencies, by which a noiselevel in a high frequency region will further increase.

SUMMARY OF THE INVENTION

An object of the present invention is to solve the above problems and toprovide a power converter apparatus capable of reliably reducingswitching noise in the power converter apparatus as compared with theprior art.

According to one aspect of the present invention, there is provided apower converter apparatus including at least one switching device, and afilter circuit. The at least one switching circuit generates analternating current (AC) voltage by switching a direct current (DC)voltage at a predetermined switching frequency (f_(SW)), and the filtercircuit converts the AC voltage from the switching circuit into a DCvoltage by low-pass filtering the AC voltage, and outputs the DC voltageto a load. The filter circuit includes first and second bypasscapacitors, and at least one inductor. The first bypass capacitorbypasses noise of a first frequency component of the AC voltage from theswitching circuit, and the second bypass capacitor bypasses noise of asecond frequency component of the AC voltage from the switching circuit.The second frequency component is lower than the first frequencycomponent of the AC voltage from the switching circuit. The at least oneinductor is inserted between the first bypass capacitor and the secondbypass capacitor. The inductance (L) of the inductor is set so that aresonance frequency (f_(r)) of the filter circuit is lower than theswitching frequency (f_(SW)) by insertion of the inductor.

Effect of the Invention

Therefore, according to the power converter apparatus of the presentinvention, it is possible to avoid complication of a circuitconfiguration, reliably reduce the switching noise in the powerconverter apparatus, and operate with a higher efficiency than that ofthe prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a circuit diagram illustrating a configuration example of apower converter apparatus according to a first embodiment.

FIG. 1B is a circuit diagram illustrating a configuration example of apower converter apparatus according to a modified embodiment of thefirst embodiment.

FIG. 2 is a circuit diagram illustrating a configuration example of anasynchronous power converter apparatus having a step-up functionaccording to a second embodiment.

FIG. 3 is a circuit diagram illustrating a configuration example of asynchronous power converter apparatus having a step-up functionaccording to a third embodiment.

FIG. 4 is a circuit diagram illustrating a configuration example of asynchronous power converter apparatus having a step-up functionaccording to a fourth embodiment.

FIG. 5 is a circuit diagram illustrating a configuration example of asynchronous power converter apparatus having a step-up functionaccording to a fifth embodiment.

FIG. 6 is a graph of simulation results of the power converter apparatusof FIG. 3 and illustrating frequency characteristics of an efficiency Efand a ripple Ie of an effective current.

FIG. 7 is a timing chart of simulation results of the power converterapparatus of FIG. 3 and illustrating respective operation signalwaveforms when a resonance frequency f_(r) does not match a switchingfrequency f_(SW) (70 kHz).

FIG. 8 is a timing chart of simulation results of the power converterapparatus of FIG. 3 and illustrating respective operation signalwaveforms when resonance frequency f_(r) matches switching frequencyf_(SW) (70 kHz).

FIG. 9 is a circuit diagram illustrating a configuration of a powerconverter apparatus according to Conventional Example 1.

FIG. 10 is a graph illustrating a relation between the resonancefrequency fr and the wiring inductance for describing a problem to besolved by the present invention.

FIG. 11 is a graph illustrating a frequency characteristic of switchingnoise indicating a problem of a power converter apparatus according toConventional Example 1.

FIG. 12 is a graph illustrating a frequency characteristic of switchingnoise indicating an action and advantageous effects obtained by meansfor solving a problem according to the present embodiment.

MODES FOR CARRYING OUT THE INVENTION

Embodiments according to the present invention will be described belowwith reference to the drawings. It should be noted that, in each of thefollowing embodiments, similar components are denoted by the samereference characters.

First Embodiment

FIG. 1A is a circuit diagram illustrating a configuration example of apower converter apparatus according to a first embodiment. Referring toFIG. 1A, the power converter apparatus according to the first embodimentis inserted between a direct current (DC) voltage source 11 and a load15. The power converter apparatus includes a switching circuit 10 and afilter circuit 30. The switching circuit 10 generates an alternatingcurrent (AC) voltage by switching the DC voltage from the DC voltagesource 11 at a predetermined switching frequency (f_(SW)), and outputsthe AC voltage to the filter circuit 30. Next, the filter circuit 30low-pass filters the AC voltage from the switching circuit to convertthe AC voltage into a DC voltage, and outputs the DC voltage to the load15.

The switching circuit 10 includes a switching device that switches theDC voltage, and a control circuit 20 that generates a drive signal fordriving the switching device with on/off control in a predetermined dutycycle.

The filter circuit 30 includes bypass capacitors 12 and 13 and inductors14A and 14B. The AC voltage from the switching circuit 10 is applied toboth of the ends of the bypass capacitor 12, and one end of the bypasscapacitor 12 is connected to one end of the bypass capacitor 13 via theinductor 14A. Another end of the bypass capacitor 12 is connected toanother end of the bypass capacitor 13 via the inductor 14B. In thiscase, the bypass capacitor 12 bypasses switching noise of a firstfrequency component (relatively high frequency component) of the ACvoltage from the switching circuit 10. The bypass capacitor 13 bypassesnoise of a second frequency component (relatively low frequencycomponent) of the AC voltage from the switching circuit 10, the secondfrequency component being lower than the first frequency component ofthe AC voltage from the switching circuit 10. The combined inductance(L) of the inductors 14A and 14B is set such that the resonancefrequency f_(r) by the filter circuit 30 is lower than the switchingfrequency f_(SW) by insertion of the inductors 14A and 14B.

That is, in the present embodiment, where C₁ represents a capacitance ofthe bypass capacitor 12, and C₂ represents a capacitance of the bypasscapacitor 13, the switching frequency f_(SW) and the resonance frequency(f_(r)) are set to satisfy the following equation:

$\begin{matrix}{{f_{SW} > {fr}} = {\frac{1}{2\pi \sqrt{L \times \frac{C_{1} \times C_{2}}{C_{1} + C_{2}}}}.}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

In the present embodiment, one of the two inductors 14A and 14B may bedeleted. In addition, the inductors 14A and 14B may be at least one of awiring inductor, a mounted inductor, and a mounted coil.

In the power converter apparatus configured as described above, thebypass capacitors 12 and 13 are connected between a power supply line,which is between the switching circuit 10 and the load 15, and a groundline in order to avoid fluctuation in the DC voltage of the DC voltagesource 11 when the power converter apparatus operates. In this case, thebypass capacitor 12 has a role of returning a high-frequency switchingnoise component generated from the switching circuit 10, and the bypasscapacitor 13 has a role of returning a low-frequency switching noisecomponent. The inductors 14A and 14B have a role of reducing theresonance frequency between the bypass capacitors 12 and 13. It shouldbe noted that the bypass capacitors 12 and 13 may be one which isconfigured to include a plurality of capacitors connected in parallel orin series in order to satisfy respective capacitances.

As described above, according to the power converter apparatus of thepresent embodiment, it is possible to avoid a complicated circuitconfiguration, reliably reduce switching noise in the power converterapparatus as compared with the prior art, and operate the powerconverter apparatus with a higher efficiency. In this case, it ispossible to select a part having a relatively small ripple as acapacitor to be inserted, suppress the overcurrent by inserting aninductor, and have a radiator of a switching device smaller than theradiator of the prior art.

It should be noted that a modified embodiment of the first embodimentcan also be applied to second to fifth embodiments.

MODIFIED EMBODIMENT OF FIRST EMBODIMENT

FIG. 1B is a circuit diagram illustrating a configuration example of apower converter apparatus according to the modified embodiment of thefirst embodiment. The power converter apparatus of FIG. 1B differs fromthe power converter apparatus of FIG. 1A in the following point.

(1) Instead of one switching circuit 10, a plurality of M number ofswitching circuits 10-1 to 10-M is included. Each of the switchingcircuits 10-1 to 10-M may separately include each of control circuits20-1 to 20-M that generate a drive signal for driving a switchingdevice, or one control circuit may drive each switching device of aplurality of switching circuits 10-1 to 10-M.

The power converter apparatus according to the modified embodiment ofthe first embodiment configured as described above has an action andadvantageous effects similar to those of the power converter apparatusaccording to the first embodiment.

Second Embodiment

FIG. 2 is a circuit diagram illustrating a configuration example of anasynchronous power converter apparatus having a step-up functionaccording to a second embodiment. The power converter apparatusaccording to the second embodiment illustrates a circuit configurationof a switching circuit 10 in detail as compared with the power converterapparatus of FIG. 1, and only differences will be described below.

Referring to FIG. 2, the switching circuit 10 includes a step-up reactor16, a switching device Q1 constituted of, for example, a MOSFET, anIGBT, or the like, a diode D1, and a control circuit 20. The DC voltagefrom the DC voltage source 11 is applied to both of the ends of thedrain and source of the switching device Q1 via a reactor 16, and thedrain of the switching device Q1 is connected to one end of a bypasscapacitor 12 via the diode D1. The control circuit 20 generates a drivesignal S1 for driving the switching device Q1 with on/off control in apredetermined duty cycle, and applies the drive signal S1 to a gate ofthe switching device Q1.

The power converter apparatus according to the second embodimentconfigured as described above has an action and advantageous effectssimilar to those of the power converter apparatus according to the firstembodiment, except for having an asynchronous step-up function.

Third Embodiment

FIG. 3 is a circuit diagram illustrating a configuration example of asynchronous power converter apparatus having a step-up functionaccording to a third embodiment. The power converter apparatus accordingto the third embodiment differs from the power converter apparatus ofFIG. 2 in the following points:

(1) instead of the switching circuit 10, a switching circuit 10A isincluded; and

(2) the switching circuit 10A includes a step-up reactor 16, switchingdevices Q1 and Q2, which are each configured to include, for example, aMOSFET, an IGBT, or the like, and a control circuit 20A.

Referring to FIG. 3, the DC voltage from the DC voltage source 11 isapplied to both ends of the drain and source of the switching device Q1via a reactor 16, and the drain of the switching device Q1 is connectedto one end of the bypass capacitor 12 via the source and drain of theswitching device Q2. The control circuit 20A generates drive signals S1and S2 for driving the switching devices Q1 and Q2 with on/off controlin a predetermined duty cycle and in synchronization in periodsdifferent from each other, and applies the drive signals S1 and S2 tothe gate of the switching device Q1.

The power converter apparatus according to the third embodimentconfigured as described above has an action and advantageous effectssimilar to those of the power converter apparatus according to thesecond embodiment, except for having a synchronous step-up function.

Fourth Embodiment

FIG. 4 is a circuit diagram illustrating a configuration example of asynchronous power converter apparatus having a step-up functionaccording to a fourth embodiment. The power converter apparatusaccording to the fourth embodiment differs from the power converterapparatus of FIG. 3 in the following points:

(1) instead of the inductor 14A, a first inductor L1 of a common modechoke coil (CMC) 17 is included; and

(2) instead of the inductor 14B, a second inductor L2 of the common modechoke coil (CMC) 17 is included.

In this case, the common mode choke coil (CMC) 17 is providedparticularly for removing common mode noise. It should be noted that twoinductors L1 and L2 may be provided instead of the common mode chokecoil (CMC) 17. In addition, the two inductors L1 and L2 may include aleakage inductance of the common mode choke coil (CMC).

The power converter apparatus according to the fourth embodimentconfigured as described above has an action and advantageous effectssimilar to those of the power converter apparatus according to thesecond embodiment, except for having a synchronous step-up function.

Fifth Embodiment

FIG. 5 is a circuit diagram illustrating a configuration example of asynchronous power converter apparatus having a step-up functionaccording to a fifth embodiment. The power converter apparatus accordingto the fifth embodiment differs from the power converter apparatus ofFIG. 4 in the following points:

(1) a bypass capacitor 18 connected in parallel with the DC voltagesource 11 is further included;

(2) another end of the bypass capacitor 13 is connected to the groundside of a load 15 via a fuse 19 that is blown when a current which islarger than a predetermined threshold current flows; and

(3) another end of the bypass capacitor 18 on the ground side isconnected to the connection point between the bypass capacitor 13 andthe fuse 19 via the second inductor L2 of a common mode choke coil (CMC)17.

In the power converter apparatus configured as described above, it ispossible to suppress the overcurrent in the bypass capacitors 13 and 18by adding the fuse 19. By providing the common mode choke coil (CMC) 17,it is possible to reduce the resonance frequency in the resonant circuitconfigured to include the combination of inductors L1 and L2 included inthe common mode choke coil (CMC) 17 with each of bypass capacitors 12and 13. The other action and advantageous effects of the presentembodiment are similar to those of the fourth embodiment.

IMPLEMENTATION EXAMPLES

FIG. 6 is a graph of simulation results of the power converter apparatusof FIG. 3 and illustrating frequency characteristics of an efficiency Efand a ripple 1 e of an effective current. The present inventorsperformed a simulation for confirming the effect of the resonancesuppression with a circuit simulator (software name: Simetrix) by usingthe circuit configuration of the power converter apparatus according tothe third embodiment of FIG. 3. Table 1 below illustrates conditions ofthe simulation.

TABLE 1 Item Numerical Value Voltage of DC voltage source 11 100 VSwitching frequency f_(sw) 70 kHz Bypass capacitor 12 2.2 nF Bypasscapacitor 13 131 μF Inductors 14A and 14B 0.21 μH to 28.8 μH (Variable)Load 15 68.2 Ω

The resonance frequency f_(r) was changed by changing the combinedinductance value of the inductors 14A and 14B. By setting the resonancefrequency f_(r) to be lower than the switching frequency f_(SW),reduction of the ripple Ie and increase in the efficiency Ef wereconfirmed. As is apparent from FIG. 7, it is shown that whenf_(r)=f_(SW), the efficiency Ef decreases and the ripple 1 e of theeffective current increases, and that by setting f_(r)<f_(SW), theefficiency Ef increases and the ripple 1 e of the effective currentdecrease as compared with that when f_(r)=f_(SW).

FIG. 7 is a timing chart of simulation results of the power converterapparatus of FIG. 3 and illustrating respective operation signalwaveforms when the resonance frequency f_(r) does not match theswitching frequency f_(SW) (70 kHz). In addition, FIG. 8 is a timingchart of simulation results of the power converter apparatus of FIG. 3and illustrating respective operation signal waveforms when theresonance frequency f_(r) matches the switching frequency f_(SW) (70kHz). As is apparent from FIG. 8, it is shown that when the resonancefrequency f_(r) matches the switching frequency f_(SW) (70 kHz), theripple current and the ripple voltage increase. Meanwhile, it is shownthat when the resonance frequency f_(r) does not match the switchingfrequency f_(SW) (70 kHz), the ripple current and the ripple voltagedecrease.

Comparison with Conventional Example 1

FIG. 11 is a graph illustrating a frequency characteristic of switchingnoise indicating a problem of a power converter apparatus according toConventional Example 1, and FIG. 12 is a graph illustrating a frequencycharacteristic of switching noise indicating an action and advantageouseffects obtained by means for solving the problem according to thepresent embodiment.

In the power converter apparatus according to Conventional Example 1shown in FIG. 11, a plurality of IGBTs is used for a power switchingdevice, and the switching frequency is 20 kHz, which is relatively a lowfrequency. In Conventional Example 1, operation is performed in a highfrequency region having a low noise level by an inductor having arelatively small inductance, the inductor connecting two bypasscapacitors.

However, in the power converter apparatus according to ConventionalExample 1, the power converter apparatus can be miniaturized and highlyefficient by using a next-generation power semiconductor switchingdevice (SiC or GaN) as a switching device for a switching circuit togenerate a high frequency. However, as the frequency increases, theswitching frequency may match the resonance frequency between the bypasscapacitors. Thus, this leads to more ripples, a lower efficiency, andshorter lifetime.

In particular, in the switching circuits 10A and 10B, when the switchingdevice in the switching circuit 10 malfunctions, the overcurrent mayflow from the bypass capacitors 12 and 13. In the present embodiment,the inductors 14A and 14B having an inductance larger than that of theprior art are arranged in a forward stage of the bypass capacitor 13having a resonance frequency lower than that of the prior art and havinga capacitance larger than that of the prior art. Then the effect of theovercurrent suppression can be obtained. Meanwhile, in ConventionalExample, the inductance of the inductor is smaller than the inductancein the present embodiment, and thus the effect of the overcurrentsuppression is small.

Meanwhile, according to the first to fourth embodiments, by the increasein the inductance of the inductor to set the resonance frequency f_(r)to be lower than the switching frequency f_(SW), it is possible to driveit at switching frequency f_(SW) at which the switching noise does notgenerate as illustrated in FIG. 12. Meanwhile, in Conventional Example2, it is driven at the switching frequency f_(SW) with a low noise levelby a decrease in the inductance to set the resonance frequency f_(r) tohigher than the switching frequency f_(SW). Although a configuration ofa switching device using a next-generation power device will promote ahigher frequency of the power converter apparatus. Then the noise levelin a high frequency region will increase in the future, it is possibleto solve these problems by using the configuration of the presentembodiments to shift to a low frequency region having a small noiselevel.

INDUSTRIAL APPLICABILITY

As described in detail above, according to the power converter apparatusof the present invention, it is possible to avoid a complicated circuitconfiguration, reliably reduce switching noise in the power converterapparatus as compared with the prior art, and operate the powerconverter apparatus with a higher efficiency. In this case, it ispossible to select a part having a relatively small ripple as acapacitor to be inserted, suppress the overcurrent by inserting theinductor, and have a radiator of the switching device smaller than theradiator of the prior art.

DESCRIPTION OF REFERENCE CHARACTERS

-   -   10, 10-1 to 10-M, 10A: SWITCHING CIRCUIT    -   11: DC VOLTAGE SOURCE    -   12, 13: BYPASS CAPACITOR    -   14A, 14B: INDUCTOR    -   15: LOAD    -   16: INDUCTOR    -   17: COMMON MODE CHOKE COIL (CMC)    -   18: BYPASS CAPACITOR    -   19: FUSE    -   20, 20-1 to 20-M, 20A: CONTROL CIRCUIT    -   30, 30A, 30B: FILTER CIRCUIT    -   D1: DIODE    -   L1, L2: INDUCTOR    -   Q1 to Q4: SWITCHING DEVICE

1. A power converter apparatus comprising: at least one switchingcircuit that generates an alternating current (AC) voltage by switchinga direct current (DC) voltage at a predetermined switching frequency(f_(SW)); and a filter circuit that converts the AC voltage from theswitching circuit into a DC voltage by low-pass filtering the ACvoltage, and outputs the DC voltage to a load, wherein the filtercircuit comprises: a first bypass capacitor that bypasses noise of afirst frequency component of the AC voltage from the switching circuit;a second bypass capacitor that bypasses noise of a second frequencycomponent of the AC voltage from the switching circuit, the secondfrequency component being lower than the first frequency component ofthe AC voltage from the switching circuit; and at least one inductorinserted between the first bypass capacitor and the second bypasscapacitor, wherein an inductance (L) of the inductor is set so that aresonance frequency (f_(r)) of the filter circuit is lower than theswitching frequency (f_(SW)) by insertion of the inductor.
 2. The powerconverter apparatus as claimed in claim 1, wherein the switchingfrequency (f_(SW)) and the resonance frequency (f_(r)) are set tosatisfy the following equation: $\begin{matrix}{{{f_{SW} > {fr}} = \frac{1}{2\pi \sqrt{L \times \frac{C_{1} \times C_{2}}{C_{1} + C_{2}}}}},} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$ where C₁ represents a capacitance of the first bypasscapacitor, and C₂ represents a capacitance of the second bypasscapacitor.
 3. The power converter apparatus as claimed in claim 1,wherein the inductor includes at least one of a wiring inductor, amounted inductor, and a mounted coil.
 4. The power converter apparatusas claimed in claim 1, wherein the inductor includes a leakageinductance of a common mode choke coil (CMC) or at least two inductorsincluded in a common mode choke coil (CMC).